Former US Ambassador to Colombia Myles Frechette said Monday that he “thought” former President Cesar Gaviria knew about campaign contributions of drug traffickers during Ernesto Samper’s successful 1994 presidential bid.

Frechetter said he believed that Gaviria hid his knowledge of the drug money in the campaign because he “wanted to protect Colombia’s image.”

Gaviria for his part denied the accusations, saying they lacked proof, and called on the United States’ government to clarify the “grave denouncement made with such outrageous lightness by Mr. Frechette.”

“It seems lacking in professionalism that an ambassador from the United States would say something so serious without saying the reasons for holding the conviction,” said Gaviria.

According to court testimony by Miguel Rodrguez, the son of and nephew of the cartel founders, the now-defunct Cali Cartel donated $10 million to Samper’s presidential bid.

Although members of Samper’s presidential campaign were convicted of complicity for the drug money campaign contribution, the former president himself was absolved after investigation.

The drug money contribution to the presidential campaign and the subsequent scandal and court proceedings severely damaged the credibility of Samper, forced the United States to revoke the visa of the then-president of Colombia, deteriorating the relationship between the two countries engaged in joint counter drug trafficking operations.

Samper is not the first Colombian president subject to Frechette’s criticism; Over the years, the former ambassador also criticized the responses of former President Alvaro Uribe over his alleged ties to Pablo Escobar’s Medellin Cartel.